1. Field of the Invention
The present invention relates to synchronizing events between electronic components in a computer system sharing a system clock, where the electronic components use internal clock frequencies different from the system clock frequency.
2. Description of the Related Art
Synchronization is a critical part of modern computer systems, as different components use different clock speeds and different sources for timing information. For example, a circuit board is often driven by a system clock and the different components on the board use higher speeds by using internal clock speeds faster than the system clock speed. In order for the different components on the board to work together, it is required that the inputs and outputs be synchronized. This synchronization is usually performed by using the system clock as reference, where the internal clock of a board component uses a frequency that is a multiple of the system clock frequency, and where the system clock rising edge coincides with the rising edge of one of the cycles of the internal clock.
Knowing when the system and the internal clocks are synchronized is therefore critical. Additionally, it is often important for the logic running inside a board component to know exactly when the system clock rising edge is appearing so the signals in the input and output lines are asserted at the right time. For example, automatic test equipment (ATE) uses the system clock to drive the tester pins, and the data has to be setup and strobed with respect to the edge of the system clock. In the case of microprocessors, their internal clocks usually run at a much higher frequencies than the one from the system clock by using internal PLL clocks that derive the internal frequencies by multiplying the system clock frequency with one of the multipliers supported in the PLL design.
Thus, the internal logic and circuitry of an electronic component must identify reliably when the system clock and the internal clock are synchronized in order to perform reliable interaction with other electronic components.
It is in this context that embodiments of the invention arise.